Air conditioning system



1953 M. e.- SHOEMAKER 2,655,793

AIR CONDITIONING SYSTEM Filed FOb. 10, 1951 Patented Oct. 20, 1953 UNITED STATES PATENT orrlca AIR CONDITIONING SYSTEM Malcolm G. Shoemaker, Doylestown, Pa., assignor to Philco Corporation, Philadelphia, Pa., a cor- I poratlon of Pennsylvania Application February 10, 1951, Serial No. 210,822

7 8 Claims. (01. 82-3) This invention is concerned with air conditioning apparatus and, more particularly, relates to novel apparatus for eflecting cooling and dehumidificatlon of circulating air.

Broadly, the invention has for its primary ob- Ject providing control, or modulation," of the capacity of an air conditioning machine in such manner that temperature conditions within a desired range may be maintained without undue sacrifice of the capacity or the machine to effect 10 the transfer of latent heat which results in condensation of undesired moisture present in the circulating air.

It is now well known in air conditioning practice that maintaining a conditioned space within the so-called comfort zone" involves control of the air dry bulb temperature and also limitation of the relative humidity prevailing within said space. For example, under summer cooling conditions, the comfort zone is frequently regarded Under high humidity conditions most frequently encountered in climates where room cooling is desirable, pull-down" oi the air temperature to 1 an acceptable value necessarily results in a very substantial increase l the relative humidity, and

removal of moisture rom the air is essential. A

relatively wide range of psychrometric conditions may exist, and control of the cooling capacity of the air'conditioning machine (as respects transfer of both sensible and latent heat) is therefore essential if the space being conditioned is to be kept within the comfort zone.

At times, particularly when the apparatus is being operated to cool a bedroom at night, the dry bulb temperature of the circulating air may drop below a desired minimum value, and it is 40 then desirable to modulate the capacity of the machin in such a way as to restore the desired temperature condition. In large installations such modulation can conveniently be provided by adding heat and/or moisture to off-set the ex-' 4 cess cooling capacity. In large installations refrigerating eiiect can also be conveniently modulated by varying the number of compressor cylinders eflective to pump refrigerant, or by manipulating dampers to regulate air flow, .or

by varying the speed of the compressor.

While the aforesaid problems exist in the case of single room, package type air conditioners, the foregoing solutions are not applicable for a variety of reasons, including cost considerations.

Most single room air conditioners utiliz a compressor having only one cylinder and it is therefore apparent that modulation of capacity, by varying the number of cylinders, is not feasible.

Cycling the motor compressor has also not proven 00 to be a practical solution. The rapid increase in humidity which usually takes place during periods or idleness of the compressor may cause the relative humidity to reach a value exceeding the comfort zone limits, even though cycling may maintain the dry bulb temperature within a satisfactory range. Further, the variation in sound level which results from cycling the unit is highly objectionable, especially in bedroom applications.

Previously, attempts have beenmade to meet the foregoing difllculties and to provide satisfactory capacity modulation of air conditioning equipment of the simpler type, and these attempts have usually involved provision of means for varying the operation of the air conditioning machine in such a way that the temperature of.v

th entire evaporator is raised to a higher value, in response to a predetermined reduction in the temperature of the circulating air. However, practice has shown this expedient to be entirely unsatisfactory in view of the fact that there is no longer suflicient limitation of humidity and it is therefore not possible to meet the comfort zone conditions. This will be understood from the fact that increasing the temperature of the entire evaporator limits the capacity of the evaporator to effect transfer of latent heat and, as a consequence, the relative humidity soon rises to an excessively high value. Attempts have also been made to meet this problem by utilizing machines having two separate refrigerating units, operation of one of which can be discontinued when reduction in total capacity is desired. Such apparatus has alsoproven unsatisfactory, because of its relatively high cost, and also by virtue of the fact that discontinuation of operation of one of the units results in variation in the sound level of the machine, As pointed out above, such variation is undesirable.

With the foregoing in mind, it is to be noted that the present invention provides apparatus for modulating the capacity of household room air conditioning machines in such manner that the total air cooling capacity of the evaporator is reduced, when the temperature of the circulating air falls to a predetermined value, and yet the apparatus is of such a character'that a portion of the evaporator continues to operate at a temperature suiflciently low to result in substantial j condensation of moisture present in the circulat- In the achievement of the foregoing general ends, the invention provides, in novel combination with the elements of an air conditioning system of known type, an auxiliary refrigeration 3 system including condenser, restrictor and evaporator portions connected in series circuit with the compressor, the condenser portion of said auxiliary system being disposed in heat exchange relation with a portion only of the main evaporator element at a region intermediate the entrance to and the exit from said element, and the evaporator portion of said auxiliary system being disposed in heat exchange relation with the high pressure side of the main refrigerating system. Means is provided for causing a portion of the gaseous refrigerant derived from the compressor to flow through the auxiliary system, with the result that the liquid refrigerant reaching the region of heat exchange, in the main evaporator element, is converted to the gaseous state, as it condenses the gas present in the auxiliary circuit, with the result that the main evaporator is deprived of liquid'.refrigerant from the region of said heat exchange to the outlet end of said evaporator. In this way part of the evaporator is rendered substantially ineffective to cool the circulating air. evaporator, however, is still provided with liquid refrigerant, and this portion therefore continues to operate at a temperature approximately equal The remaining portion,of the to the normal (unmodulated) temperature of the over-all evaporator. The extent of the evaporator portion which is thus deprived of liquid refrigerant may be varied to any desired degree and, in a preferred embodiment of my invention, there is also included means for reducing the compressor suction pressure to a value such that the part of the evaporator which remains active as a heat transfer element will operate, under conditions of modulation, at a temperature somewhat lower than the normal operating temperature.

The manner in which the foregoing and other objects and advantages of the invention may best be achieved will be clearly understood from a consideration of the following description, taken in conjunction with the accompanying drawing, in the single figure of which there appears a diagrammatic representation of an air conditioning machine embodying the modulating apparatus of my invention.

Making more detailed reference to the drawing, thereis diagrammatically illustrated an air conditioning or refrigerating system including a pair of heat exchangers I0 and II, which may be of known finned coil type. A compressor I2 is connected in series flow circuit with said heat exchangers through the agency of suitable conduits including the capillary type restrictor shown at l3, and the suction and discharge passages which appear in the drawing at M and I5, respectively. As will be understood, the capillary tube.

l3 and portions of the suction line I 4 may be placed in heat exchange relation, but such disposition of these elements has been omitted from the drawing in the interest of simplicity in illustration.

The equipment further includes switching apparatus, shown diagrammatically at It, and through the agency of which the motor of compressor I2 may be placed across the line L. As will be understood, provision is made in such a machine for forcing air over the heat exchangers or coils, and to this end suitable fans and motors are commonly employed. These elements of the apparatus have been omitted from the drawing, since illustration and description thereof are not necessary to an understanding of the present invention, but the direction of air flow through the 4 heat exchanger III, which comprises the evaporator of the machine, should be understood as being perpendicular to the face of the evaporator as shown. While a showing of the air conditioner cabinet has also been omitted, it will be appreciated that a cabinet would be provided having partition means serving to divide the same into separate chambers housing the evaporator Ill and the condenser II. A dashed line appears in the figure, and that portion of the apparatus which lies to the left of said dashed lines functions as an evaporator during cooling of the room, as above mentioned. As is apparent from he legend, this portion of the apparatus is dlsm ed on the indoors side of said dashed line. The condenser and preferably the compressor are, as indicated, disposed out-of-doors.

The construction of the machine, described Just above, is conventional in nature, and its operation need not be set forth in detail herein except insofar as the elements thereof cooperate with and are affected by the novel capacity modulating means now to be described.

' In particular accordance with the present invention, there is provided an auxiliary refrigeration circuit or system which includes a condenser portion I1 and an evaporator portion l8 connected in series circuit with the compressor l2, through a capillary type restrictor I 9 and through suction and feed conduits shown at Ma and He, respectively. The direction of refrigerant flow through the system, under normal operating conditions, is represented by arrows shown in solid lines, whereas the refrigerant flow through the auxiliary system asdesignated by arrows shown in broken lines.

Flow of refrigerant through the auxiliary system is established in response to a change in the condition of the air circulating past the evaporator I0 and, preferably, in response to a predetermined reduction in the temperature of the circulating air. To this end there is included a temperature-sensitive switch device 20 responsive to the pressure of a vaporizable fluid contained within a feeler bulb 2|, the latter being so disposed as to respond to the temperature of the air as it flows into contact with th evaporative heat exchanger Hi. When this temperature has fallen to a predetermined lower limit switch device 20 is closed, with the result that a valve mechanism 22 which preferably takes the form of asolenoid-actuated valve of a type now well known, is opened and a portion of the gaseous refrigerant derived from the compressor flows through the feed conduit l5a, and thence through the condenser portion I1 and the capillary restrictor i9. It will be understood, of course, that while automatic control is preferable, the invention also contemplates use of a manually operable valve in place of the solenoid-actuated valve 22, if such be desired.

Although the evaporator may take other forms, preferably, and as illustrated, it is of the continuous series coil type. In any event it includes a loop or region, shown diagrammatically at 23, which is disposed in high heat exchange relation with the aforesaid condenser portion I! of the auxiliary refrigeration system. Selection of the portion or region of the evaporator tubing to be disposed in such heat exchange relation, determines the extent to which operation of the auxiliary refrigeration system will modulate the cooling capacity of the evaporator I0. For exemplary purposes the loop 23 is shown as disposed approximately midway between the inlet and outlet ends of evaporator l0, and with such an arrangement it is possible to reduce the over-all air-cooling capacity of the evaporator by about one-half. when the solenoid valve 22 has been opened, in response to the aforesaid reduction in temperature of the circulating air, the gaseous refrigerant introduced into the auxiliary system through the feed conduit I50, is condensed in condenser portion H, with resultant vaporization of liquid refrigerant passing through the evaporator heat exchange loop 23. Liquid refrigerant thus provided in the auxiliary circuit is fed through the capillary tube 19 and delivered to evaporator portion I! wherein, by virtue of heat exchange between the said portion and the warm gaseous refrigerant flowing through the conduit 15 of the main refrigeration circuit, the liquid emitted from the capillary tube I9 is re-evaporated, after which it returns to the compressor through suction conduit Ila.

Under the described conditions of capacity modulation, a portion of the gaseous refrigerant derived from the compressor l2 continues to flow through feed line 15 and into the condenser II. where it returns to the liquid state. The resultant liquid refrigerant, of course, is passed through capillary tube l3 of the main refrigeration system and is delivered to evaporator 10. In the evaporator, a portion of the liquid volatilize-s in those passes" of the evaporator tubing which lie to the inlet side of the above-mentioned loop 23, with the result that said passes are refrigerated and maintained at a temperature approximately equal to the temperature prevailing at the evaporator under normal unmodulated conditions. However it will be observed that a section only of the evaporator is thus refrigerated, and that those tubing passes which lie between the loop 23 and the outlet end of the evaporator are deprived of liquid refrigerant, by virtue of the heat exchange which is, concurrently, resulting in condensation of refrigerant flowing through the auxiliary condenser portion. As will now be understood, any passes of tubing which lie to the outlet side of the loop 23 will be relatively ineffective to cool circulating air, and the total air cooling capacity of the evaporator is correspondingly reduced. As a consequence of the aforesaid reduction in liquid refrigerant present in the main system, the total air-cooling capacity of the evaporator is reduced, and the temperature of the circulating air therefore tends to return to a desired normal value determined by the balance between the ambient conditions and the modulated capacity of the evaporator. Upon attaimnent of a predetermined upper temperature limit, the switch device 20 is again opened and the machine returns to normal operation.

As will now be appreciated, under conditions of modulation, that is, when refrigerant is flowing through the auxiliary refrigeration system, the evaporator tubing portions which lie to the inlet side of loop 23 will be maintained at a temperature at least as low as the normal operating temperature of the entire evaporator and, since this temperature is well below the dew-point temperature of the air passing in contact with the evaporator 10, considerable transfer of latent heat is effected and the reduction in humidity which is necessary to the maintenance of comfort conditions is continued.

It is a articular feature of my invention that the apparatus is self-compensating when operating'under the modulated condition, in that the suction pressure of the over-all system is automatically maintained at a value such that por- 6 tions of the evaporator l0 which still include liquid refrigerant continue to operate at a temperature in the region of the normal value. This compensation results from the fact that condensation of refrigerant in condenser portion I! of the auxiliary system deprives the main system of an equivalent quantity of refrigerant, thus reducin the flow in said main system. If too great a reduction of flow in the main circuit tends to take place, a lesser quantity of liquid refrigerant is available in the loop 23 of evaporator 10, with the result that less refrigerant is condensed in portion I1, and a greater quantity of refrigerant is accordingly again shifted to'the main circuit. The described action is very pronounced when the solenoid valve is first opened. At this time there is, temporarily, a rapid rise in suction pressure due to the sudden addition of heat to the evaporator 10. .However the suction pressure begins to fall almost immediately, since less refrigerant is available in the main circuit, and the pressure levels out at a stable value after a plurality of oscillations of progressively diminishing amplitude. Thus the suction pressure of the system stays in balance, even under conditions of modulation, because the heat transfer taking place at the auxiliary evaporator portion I8 is balanced by the heat exchange taking place at loop 23, under steady state conditions. This is so even though the capillary restrictions may not be exactly balanced, capillary tubes being capable of passing only a fraction of the amount of refrigerant in the gaseous state, by weight, that can be passed in the liquid state.

To meet certain operating conditions, it may be desirable to maintain at a portion of the evaporator H) a temperature somewhat lower than the temperature which prevails when the system is operating under normal unmodulated conditions. This result can be readily attained by use, in the auxiliary system, of an accumulator disposed as shown at 24. The suction pressure of the over-all machine will be reduced to the extent that the effective quantity of refrigerant active in the apparatus is lessened by collection of a portion thereof in the accumulator 24.

From the foregoing description it will be understood that the present invention provides air conditioning apparatus of extremely simple type in which there is included means for reducing the total air cooling capacity of the evaporator, while yet maintaining a portion of said evaporator at a temperature sufficiently low to continue substantial condensation of excess moisture present in the circulating air.

While a preferred structural embodiment of my invention has been illustrated and described, it is to be borne in mind that said embodiment is susceptible of modification, without departing from the spirit of this invention. For example, the evaporator I0 and its heat exchange portion 23 need not nece sarily be of the type disclosed herein. Further, it will be apparent that the location of the auxiliary heat exchanger I8 may be varied if desired, and that the location of the heat exchange I'l-23 is a matter of choice dependent upon the amount of capacity reduction which is desired. It is also to be borne in mind that while the primary utility of the apparatus of the invention is to condition air'within a room, the prnciples of the invention might also be embodied in equipment utilized to control the condit on of air within the insulated cabinet of a refrigerator. However it will be understood that the invention contemplates such changes and 7 modifications as properly come within the scope of the pp nded claims.

I claim:

1. In air conditioning equipment, a main refrigeration system including compressor, con denser. restrictor and evaporator elements so connected in series flow circuit that condensation of refrigerant occurs in said condenser element, and evaporation of refrigerant occurs in said evaporator element with consequent cooling of the-circulating air, and apparatus for reducing the total air-cooling capacity of said evaporator element while yet maintaining a portion of the evaporator element at a temperature sufliciently low to result in substantial condensation of moisture present in' the circulating air, said apparatus comprising: an auxiliary refrigeration system including condenser, restrictor and evaporator portions connected in series circuit with said compressor element, said condenser portion being disposed in heat exchange relation with a portion of said evaporator element at-a region intermediate the entrance to and the exit from said element, and said evaporator portion being disposed in heat exchange relation with a portion of the high pressureside of said main system in which gaseous refrigerant is normally present; and means effective to cause a portion of the gaseous refrigerant derived from said compressor element -to flow through said auxiliary system.

, 2. In air conditioning equipment, a main refrigeration system including compressor, condenser, restrictor and evaporator elements so connected in series flow circuit that condensation of refrigerant occurs in said condenser element, and evaporation of'ref rigerant-occurs in said evaporator element with consequent cooling of the circulating air, and apparatus for reducing the total air-cooling capacity of said evaporator element while yet maintaining a portion of the evaporator element at a temperature sufliciently low to result in substantial condensation of moisture present in the circulatingair, said apparatus comprising: an auxiliary refrigeration system including condenser, restrictor and evap-,-

orator portions connected in series circuit with said compressor element, said condensor portion being disposed in heat exchange relation with a portion of said evaporator element at a region intermediate the entrance-to and the exit from said element and said evaporator portion being disposed in heat exchange relation with a portion of the high pressure side of said main system in which gaseous refrigerant is normally present; and valve means responsive to the temperature of the circulating air and effective to cause a portion of the gaseous refrigerant derived from said compressor to flow through said auxiliary system.

3. Air conditioning equipment in accordance with claim 1, and further characterized in that the said evaporator portion is disposed-in heat exchange relation with a portion of the high the total air-cooling capacity of said evaporator while yet maintaining a portion of the evaporator at a temperature sumciently low to result in substantial condensation of moisture present in the circulating air, said apparatus comprising: an auxiliary refrigeration system including condenser, restrictor and evaporator portions connected in series circuit with said compressor element, said condenser portion being disposed in heat exchange relation with a portion of said evaporator element at a region intermediate the entrance to and the exit from said element and said evaporator portion being disposed in heat exchange relation with a portion of the high pressure side of said main system in which gaseous refrigerant is normally present; means effective to cause a portion of the gaseous refrigerant derived from said compressor element to flow through said auxiliary system; and means for accumulating a portion of the liquid refrigerant flowing from the said condenser portion of the auxiliary system; whereby to reduce the effective quantity of refrigerant with resultant decrease in the compressor suction pressure.

5. In air conditioning equipment,'a main refrigeration system including compressor, condenser, restrictor and evaporator elements so connected in series flow circuit that condensation of refrigerant occurs in said condenser element and evaporation of refrigerant occurs in said evaporator element with consequent cooling of the circulating air, said evaporator element in cluding a section of series tubing having an inlet end into which is delivered liquidrefrigerant flowing from said restrictor and an outlet end from which gaseous refrigerant returns toward said compressor, and apparatus for reducing the total air-cooling capacity of said evaporator element while yet maintaining a portion of the evaporator element at a temperature sufliciently low to result nsubstantial condensation of moisture present in the circulating air, said apparatus comprising:

an auxiliary refrigeration system including condenser, restrictor and evaporator portions connected in series circuit with said compressor, said condenser portion being disposed in heat exchange relation with the series tubing of said evaporator element at a region intermediate the said inlet and outlet ends of the latter. and said evaporator portion being disposed inheat exchange relation with a portion of the high pressure side of said main system in which gaseous refrigerant is normally present; and means effective to cause a portion of the gaseous refrigerant derived from said compressor to flow through said auxiliary system.

6. Air conditioning equipment in accordance with claim 5, and further characterized in that the stated region of heat exchange between the condenser portion of said auxiliary system and the series tubing of said evaporator element is disposed substantially midway between the inlet and outlet ends of the latter.

1 MALCOLM G. SHOEMAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,956,707 Carrier May 1, 1934 2,049,625 Ruppricht Aug. 4, 1936 2,080,358 Kucher May 11, 1937 2,179,734 Ullstrand Nov. 14, 1939 2,196,473 Ploeger Apr. 9, 1940 

